Methanesulfonic acid alkyl esters have been widely used as production intermediates of various fine chemicals. For example, it is known that a methanesulfonic acid isopropyl ester is used as an intermediate of an agricultural fungicide.
As a method for producing a methanesulfonic acid ester such as isopropyl methanesulfonate, methods described in the following documents are known. That is, Patent Document 1 discloses a methanesulfonylation (mesylation) reaction in which an alcohol is allowed to react with methanesulfonyl chloride in an organic solvent in the presence of a predetermined tertiary amine catalyst.
Non-patent Documents 1 and 2 disclose a method of methanesulfonylation conducting by reacting an alcohol with methanesulfonyl chloride in the presence of triethylamine.
In the above production methods, excess tertiary amine that is not used for the reaction remains in the reaction mixture immediately after the reaction. In order to remove the excess tertiary amine from the reaction mixture, conventionally, the reaction mixture is washed with aqueous hydrochloric acid.